It is generally considered that in allergic asthma and other atopic diseases of man or anaphylactic shock in animals, various chemical mediators are released from lung and other tissues and cause difficulties in living bodies, such as the constriction of smooth muscles, e.g., bronchi, pulmonary artery, etc., and the enhancement of vascular permeability in the skin. As such chemical mediators, there are histamine and SRS-A. Histamine plays an important role in guinea pig anaphylactic shock but not in allergic asthma in man (Eiser, "Pharmacology and Therapeutics", 17, 239-250 (1982)), whereas a number of evidences suggest that SRS-A is the most important chemical mediator of allergic asthma in man (Brocklehurst, "Journal of Physiology", 151, 416-435(1960); Austen and Orange, "American Review of Respiratory Diseases", 12, 423-436(1975); Adams and Lichtenstein, "Journal of Immunology", 122, 555-562(1979)).
The development of the medicaments for prophylaxis, elimination and reduction of immediate hypersensitivity reactions was performed aiming at inhibiting the production and release of such chemical mediators or antagonizing the action of these chemical mediators. As an inhibitor of histamine release, disodium cromoglycate is well known and as an inhibitor of actions induced by histamine, various anti-histaminics are commercially available. On the other hand, SRS-A is known as a slow reactive and long acting chemical mediator while histamine is a rapid acting and short acting chemical mediator, and it has recently been recognized that SRS-A is a mixture of Leukotriens C.sub.4, D.sub.4 and E.sub.4 the structure of which have been clarified by Dr. Samuelsson. SRS-A, i.e., Leukotriens are lipoxigenase products of polyunsaturated fatty acids (in particular, arachidonic acid) and it has been reported that SRS-A has various activities such as enhancement of mucus production, reduction of mucociliary transport, coronary artery constrictor action, reduction of cardiac contractility, etc., besides the aforesaid action in the character of chemical mediator in immediate hypersensitivity reactions.
To delineate the dynamic roles of SRS-A and to modulate its actions in various phthological conditions, obviously it would be highly desirable to have a specific and in vivo active receptor antagonist. Furthermore, it is clinically desirable to prepare an orally active compound. FPL 55712* of Fisons shows potent anti-SRS-A activity in isolated tissues (Augstein et al, Nature New Biol., 245, 215-217(1973)). However, its biological half life is very short and its absorption by oral route is very poor (Sheard et al, Mongr. Allergy, 12, 245-249(1977)). ##STR3##
Accordingly, it has been desired to develop medicaments capable of inhibiting the production and release of SRS-A or medicaments capable of antagonizing these actions of SRS-A, in particular, the aforesaid medicaments effective in oral administration.